Method and apparatus for producing spiral broaches



W. O. NIXON June 6, 1950 METHOD AND APPARATUS FOR PRODUCING SPIRAL BROACHES 3 Sheets-Sheet 1 Filed Oct. 18, 1945 INVENTOR.

WILLIAM O.NIXON ATTORNEYS June 6, 1950 w. o. NIXON 2,510,830

METHOD AND APPARATUS FOR PRODUCING SPIRAL BROACHES Filed Oct. 18, 1945 3 Sheets-Sheet 2 INVENTOR.

ATTORNEYS June 6, 1950 I w. o. NIXON 2,510,830

I METHOD AND APPARATUS FOR PRODUCING SPIRAL BROACHES Filed Oct. 18, 1945 s Sheets-Sheet 5 INVENTOR.

WILLIAM O. NIXON ATTORNEYS Patented June 6, 1950 siren "sma- METHODAND APPARATUS SPIRAL BRIQACHES V I r L fast Detroit, Mlch assignor,

a ign'rnents, to Turner Bros. Inn,

. 1 his "inven ionijltelats e. lv '11? and refers more particularlyto broac es helical teeth v.

M In instances 'whereit is'de'sirabl'e or 'esse'n al to broach round holes with a shearing out, a breach is advantageouslyemployed haying a continuous helical tooth provided 'with a fade or rake angle wh q z.is .pgsit ye and. rariesi pe d n upon th hara t ri s .thamgt liq beset-4 11 .Q vsrindiahe mot er: rq c wi h a:

positive rake angle at the cuttin edge, iti is essential to reach back of the cutting edge of the tooth with the;peripheral-portion;of the grinding wheel in a rhanner'to avoid contact of the wheel with the cutting edgeo'fthebroach tooth. This is usually accomplished by (using a smallgrinding wheel in comparison to the diameter'of'thebroach and in tiltingthe grinding wheel to take advantage to the sharp 'radiu's 5f the periphery of the wheel, Thedifiiculty in accomplishing this operation increases-asthe diarneter of the breach decreases.andinlcases where the diameterof the broach is one inch or less, very; little clearance is "a ab 'iqr e ridin' wh lhl a it, ha e n nsi e e impr ct cal i e a t grind helicalteeth on a 'small di'ameter broach with an u der ut be u eiths e "o thee s hee Pe m i e-1's Q $31 1 as .3133? it tiQ W impossible 'to-m'aintain'a sharp and free cutting "edgeon the Wheel.

Itis an objeot of this invention to overcome the above difificulties by providing a method and apparatus for manufacturing spiral broaches of practically any size with'helica'l "teeth having a positive rake or'faceangle. In accordance with t s i hv ti nyspira 11211 2361 6 a ,small a 1120 {of an' inch in diameter may be ground with a posi- "tive rake'an'glerat'the cutting edgewhile employ- ..ingwheels ofxsubstantial diameter. In fact, the

' diarneter;of the fwhee1 u'sed'isfnot restricted by the dia eter of thejbroach. The result is that wheelsmaybe usedwhich will retain'thei'r cutting accuracy over a long period of use with infrequent dressin g. V Th gfor go ns Well on1 g a spiral bro'ach his inv nt ,7

evaudhal view or the asother m b are table a ns-1 "f a W o 65 "5 oiaiin's. ((51. 51:71)

"cordingly. not shown herein.

FOR i nonhersa Figure 4 is'an exaggerated fragmentary sectional view showing [a portion ofsa grinding Wheel inoperative relation to a part o'fthe broach';

Figure 5115a perspective view of'a part of the broach forming the subject' zhatter of this invention; Q I

Figure 6 is a diagram showing 'a developmental? "one'of the broach teeth; H

Figure 7 is1a;.diagram'of the broachltoothface from which'Figure 6 was projected; and

Fi -ur'e e is also a 'diagramrprojected from Figure 6. The method of producing broaehe's having heli- 'c'al teeth'with a'positiverake angle at the cutting edge will 'bemore fully understood from a brief description-of the apparatus employed to carry out'the various steps of theimethod. IHoWeverJit will benotedas this descriptionproceedsthat the method may be-practiced with various differe'nt types of a paratus-and is'bynom'e an's limitedto the particular equipment shown inthe drawings.

With the foregoing in view, reference is new made more'in detail to Figures 1'to 3 inclusive ifi the drawings. n. detail, the reference'cnaracter "l0 indi'c'ates'a suitable ba'se having an upwardly projecting inclined portion H aton'e' dgej ffor supporting a slide I2; The bottom of-th'e-s'lide P2 ,is fashioned 'to-form a dovetail aswm n'e'xtends for the full ljengthfof the slide'and slidably "engages in a correspondingly shaped recess 14 formed inthe topsurface of the portion .ll. Qne end'of the slide 12 is provided withya centerlfi and the opposite end of the slide carries a co- "operating center t6 aligned with the center fii.

' 'Th e' tvvo centrs cooperate to rotatablyfsupporta Work blank or a broach H tobe grouhdand the center It is supported in a suitablernannervlnot shown) on the slidefor adjustment 'towar dwand awayirom the center it, During grinding of the br q 'lwhelatter is fitdlftla fifi ve lin [12 3116. the slide is s' ynchronously fedlaterally rel t ve, to the g indin whe y nism which forms no, part of this invention and is "acbase' lfl, also supportsagrifid hg the r slide designed for movemem tcsward and, aw from .the broach at. f rst grindin WheeLisseCUredin the usfua1 manner to ajr atable shaft v 19 having the bl pds ite ends journ'alled on aca'rriage 20 and rotatable at thedesifefd speed byg'any suitable mechanism-not shown hiin. The. Carriage 2D is guided to a'ridfihin the breach .l'l byadovetailprojection 2130i; the .bo tqm of th ca ri e and a c fr sri j d 8 -sha lild groove 22 formed the tap SurfaCe bf the base It. In actual practice, the carriage with the grinding wheel thereon is slidable back and forth along a path extending at an angle to a plane BB, including the axis of the broach or centers and Hi. This angle is indicated in Figure 1 of the drawings by the character A and is sufficient to provide ample clearance between the tooth 23 on the broach and the cutting edge 23 of the wheel upon withdrawing the wheel from the broach.

Although the path of sliding movement of the grinding wheel is inclined with respect to the plane 28-3 of the broach for the purpose set forth, nevertheless, the axis of rotation of the grinding wheel or shaft l9 lies in a plane parallel to the plane BB. However, as shown in Figure 2 of the drawings, the axis of the broach is inclined in the plane 3-13 with respect to the axis of the grinding wheel at an angle S which is necessarily greater than the helical angle H of the spiral tooth on the broach. The above relative position of "the broach and grinding wheel is important since it provides for grinding the face of the tooth along the line indicated in Figure 4 of the drawings by the reference character 26 and imparts a positive rake to the cut ting edge of the tooth 25.

When the broach is supported by the centers on the angle indicated by the character S, aninterference ordinarily develops between the grinding wheel I8 and the cutting face of the tooth 25 on the broach. This interference usually takes place at the outside diameter of the tooth and results in destroying the cuttin edge as well as the rake on the tooth. In order to overcome this objection, the face 21 of the grinding wheel l8 adjacent the cutting edge is dished at an angle indicated by the character A. In other words, the face 21 of the grinding wheel 18 occupies a plane parallel to the path of travel of the carriage 20. The angle A may be relatively small and need not exceed five degrees. The periphery of the grinding wheel [8 is dressed or otherwise formed to taper inwardly from the cutting edge 23 and conform to the desired clearance face or flank 28 of the toothto be formed.

Figure 5 of the drawings illustrates an exaggerated view of a typical sixteen pitch double lead broach having a diameter of one-eighth of an inch and having a helical angle H of seventeen degres, forty minutes. The desired rake angle of the cutting face of the helical tooth is approximately a positive eight and one-half degrees. This rake angle is obtained bysetting the broach at an angle in the plane B--B of nineteen degres, forty mintues relative to the axis of the grinding wheel l8. 7 1

With the above in view, reference is now made to Figures G, 7 and 8 of the drawings, wherein the line 30 indicates the helix curve of'the outside edge of the broach tooth. The curve crosses the center line 3| of the broach at the true helical angle H, which is 17 in this case. The maximum angle S is derived between the points 32 .and 33, where the periphery of the broach 34 intersects the periphery 35 of the grinding wheel. In this case, we are not using the maximum angle. The line 31 shows the helical curve at the root of the broach tooth. The periphery 35 of the grinding wheel. contacts the line 3'! at the point 38 only, shown in Figure 7 of the drawing. The lines 49 .and 50 are helical curves at intermediate diameters 39 and 40, respectively, on the tooth face which come in contactwith theperiphery 35 of the grindingwheel at the poinl 4! 4 and 42, respectively. As the broach is rotated and synchronously fed in the manner previously stated, the points 4| and 42 move laterally and rotatively to the points 43 and 44, respectively, in the same manner as the point 32 moves to point 45. This action provides the undercut or positive rake shown in Figures 4 and 8 of the drawings.

The angle S may be approximated by the formula 2L :0 Tan m an where L is the lead of the broach tooth per broach diameter and angle X (shown in Figure 7 of the drawings) is the acute angle between the center line 3| of the broach and the line 46. The line 41, although shown as a straight line, is considered for calculating purposes the periphery of the grinding wheel, and the line 46 extends from the geometric center of the broach to the point of intersection between the periphery 34 of the broach and the line 41.

The angle :11 may be determined by the formula o Cos of angle a2= The rake angle formed on the broach tooth by setting the broach at the angle S may be determined by the formula tan S secant :v-tan fl tan x where H is the true helical angle of the broach tooth and may be determined by dividing the lead per inch of broach diameter by pi or 3.1416.

The arrangement is such as to enable accurate- 1y grinding a small diameter broach with a helical tooth having a positive rake and enables broaching a hole with a shearing cut to very close tolerances. Owing to the specified relationship between the broach and axisof the grinding wheel during the grinding operation, the helical tooth is undercut .to provide the required positive rake angle with a grinding wheel of substantial diameter. Grinding wheels having diameters of 12, 18, 24 or more inches may be successfully used on breaches as small as .020 diameter. The ratio between the small diameter broach and the relatively large diameterg rinding wheel is so great that the cutting edge 23. of the wheel. passing through the broach teeth forms substantially a, straight line. This feature contributes to the accuracy of the broach and renders it possible to maintain the cutting edge ofthe wheel over .a longperiod of use, V i a What I claim as my invention is:

l. The method of forming a broach. with a helical tooth having an oblique flank anda i ace with a positive rakefrom .the cutting .edgethereof; comprising arranging a rotary dished. grinder wheel and broach stock in intersecting relation to each otherwith theirrespectiveaxes of rotation in parallel planes but .crossingrat an, oblique angle to each other,. the peripheral surface. of said grinder wheel being at anoblique angle-to its axis and the axis of the broach stock .to fashion the flank of the tooth and the dished surface of Positive rake ly about its axis with respect to said grinder wheel.

2. The method of forming a broach with a helical tooth having an oblique flank and a face with a positive rake from the cutting edge thereof; comprising arranging a rotary dished grinder wheel and broach stock with their respective axes of rotation in parallel planes but crossing at an oblique angle to each other, the peripheral surface of said grinder wheel being at an oblique angle to its axis and the axis of the broach stock to fashion the flank of said tooth and the dished surface of said wheel being opposite the rake face of said tooth to provide clearance for the cutting edge thereof, relatively moving said grinder wheel and broach stock into or out of engagement with each other through a path which is at a slight angle to a plane perpendicular to the aforesaid planes, advancing said broach stock helically about its axis with respect to said grinder wheel when in full engagement with the latter, whereby the peripheral edge portion of said grinder Wheel will cut the rake in the face of the tooth without interference with the cutting edge thereof.

3. The method of forming a broach with a helical tooth having an oblique flank and a face with a positive rake from the cutting edge thereof; comprising arranging a rotary dished grinder wheel and broach stock in intersecting relation to each other with their respective axes of rotation in parallel planes but crossing at an oblique angle to each other which is somewhat greater than the helix angle of the tooth to be formed, the peripheral surface of said grinder wheel being at an oblique angle to its axis nd the axis of the broach stock to fashion the flank of the tooth and the dished surface of the grinder wheel being opposite the rake face of the tooth to provide clearance for the cutting edge thereof, and advancing the broach stock helically about its axis with respect to the grinder wheel, whereby the peripheral portion of said grinder wheel will cut the rake in the face of the tooth, without interference with the cutting edge of said tooth.

4. Apparatus for forming a broach wth a helical tooth having a positive rake angle in the face thereof; comprising a dished grinder wheel, means rotatably supporting a length of stock from which a broach is to be formed with its axis of rotation located in a plane parallel to a, plane having the axis of rotation of the grinder wheel therein, said axes crossing at an oblique angle to each other, and the peripheral portion of said wheel intersecting said broach stock, and means for advancing said broach stock helically about its axis with respect to said grinder wheel and towards the dished surface thereof, whereby the peripheral edge portion of the grinder wheel will cut the rake in the face of the tooth without interference with the cutting edge thereof.

5. Apparatus for forming a broach with a helical tooth having a positive rake angle in the face thereof; comprising a base, a dished grinder wheel and a holder for a length of broach stock mounted on said base with the axis of rotation of said grinder wheel and the longitudinal axis of the broach stock respectively arranged in spaced parallel planes and crossing at an oblique angle to each other, a carriage for advancing said broach stock holder and broach stock to move the latter helically about its axis and towards the dished surface of said grinder wheel when in engagement therewith to develop the helical tooth, and a carriage for moving said grinder wheel at a slight angle to its plane of rotation into and out of in-v tersecting engagement with said broach stock, thereby avoiding interference with the cutting edge of said tooth.

WILLIAM O. NIXON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 230,715 Penney Aug. 3, 1880 1,233,543 Benicke July 17, 1917 1,275,218 Calkins Aug. 13, 1918 1,339,657 Lapointe May 11, 1920 1,473,086 Davidson Nov. 6, 1923 1,659,226 Wildhaber Feb. 14, 1928 1,662,078 Severson Mar. 13, 1928 1,669,887 Wildhaber May 15, 1928 1,722,023 Streby July 23, 1929 1,867,213 Douglas July 12, 1932 1,881,705 Lapointe Oct. 11, 1932 2,048,520 Schurr July 21, 1936 2,162,758 Shotey June 20, 1939 2,217,045 Faulder Oct. 8, 1940 2,292,900 Schmidt Aug. 11, 1942 FOREIGN PATENTS Number Country Date 4,068 Great Britain Feb, 17, 1911 222,937 Great Britain Oct. 7, 1924 547,347 France Sept. 20, 1922 

